The present invention relates to a press plate positioning apparatus for positioning a press plate at a predetermined position on a drawing board in an automatic drawing machine for forming reference punch holes in the press plate and drawing register marks thereon.
When a picture pattern is not accurately printed on a press plate or the press plate is not properly mounted on a plate cylinder for printing in a rotary press, especially a multicolor press, printed pictures with good registration cannot be obtained. Conventionally, punch holes are formed at edge portions of the press plate. With reference to the punch holes, the picture pattern is printed on the press plate, and the press plate is mounted on the plate cylinder. More particularly, after the punch holes are formed in the press plate, cross-shaped register marks are drawn on the press plate with reference to the punch holes. The register marks of a film are then aligned with those of the press plate, and the picture pattern is printed on the press plate. Furthermore, when the press plate is to be mounted on the plate cylinder, reference pins are fitted in the corresponding punch holes. When the press plate is mounted in position, the two ends thereof are held by a plate lock up device and the reference pins are removed from the punch holes. In addition, when multicolor printing is performed, registering is adjusted after the impression of the register marks is checked.
The punch holes and the register marks are simultaneously formed in a conventional automatic drawing machine. The conventional automatic drawing machine comprises drawing board, a pen head arranged above the drawing board and movable in all directions, and a punching machine which is mounted on a frame for fixing the drawing board and which forms a plurality of punch holes. When register marks are to be drawn on the press plate, the press plate is fixed in position on the drawing board and punch pins of the punching machine are vertically moved by an air cylinder or the like to form punch holes. Thereafter, the pen head is driven in accordance with the drawing pattern stored in a memory to draw the register marks.
In this case, in order to make sure that the length between the edge of the press plate and the punch holes is correct, the press plate must be accurately positioned with respect to the punching machine fixed on the frame. In addition, the distance between the edge of the press plate and the punch holes varies in accordance with the type of printing press. There are generally three or four types of conventional printing presses, and the press plate must be accurately positioned for each type.
A conventional automatic drawing machine of this type has a positioning apparatus operated such that a movable stopper thereof abuts against the edge of the press plate. However, in the conventional positioning apparatus, a positioning error exceeds an allowable value due to insufficient rigidity of the stopper. In addition, the positioning operation is cumbersome and time-consuming, or results in an erroneous operation. Positioning precision depends on precision of individual operators. As a result, satisfactory positioning precision and operability cannot be obtained with the conventional positioning apparatuses.